Circuit for audio playback and for hands-free operation in a motor vehicle

ABSTRACT

The invention relates to a circuit having at least a first electroacoustic transducer (LSL, LSR) for converting electric signals into acoustic signals, a second electroacoustic transducer (MIC) for converting acoustic signals into electric signals, a program-controlled signal processing device (SPU) coupled to said transducers (LSL, LSR, MIC) to process the signals it supplies to the control device and a program storage (ROM) to store a program (AUM) for audio playback of a program (HFM) for hands-free operation for the signal processing device (SPU), wherein, the program (HFM) for hands-free operation is loaded in the signal processing unit and executed by latter in hands-free mode while the program (AUM) for audio playback is loaded in the signal processing device (SPL) and executed by the latter in the audio playback mode.

[0001] The invention relates to a circuit for audio playback and hands-free operation in a motor vehicle.

[0002] Today, audio systems including CD players, radio receiver units, output stages, and loudspeakers have become standard equipment in motor vehicles. More recently, mobile communications equipment (both permanently installed and mobile with fixed interface) has found increasing acceptance in motor vehicles. Up to now, the two systems have been installed in the vehicle as completely separate systems, with the result that the required expense for materials and installation is very high.

[0003] The goal of the invention is to present a circuit which is capable of providing both audio playback and hands-free operation, and which is low in cost.

[0004] The goal is achieved by a circuit according to claim 1. Embodiments and further modifications of the inventive concept are the subjects of the subclaims.

[0005] The advantage of the invention is the fact that the expense and complexity of the circuit are significantly reduced, and the hands-free speech quality is improved, using an approach in which an existing signal processing unit is employed that has greater computing power than the signal processing units employed in mobile communications equipment.

[0006] This advantage is achieved specifically by a circuit for audio playback and for hands-free operation in a motor vehicle having at least a first electroacoustic transducer to convert electrical signals to acoustic signals, and a second electroacoustic transducer to convert acoustic signals to electrical signals. In addition, a program-controlled signal processing unit coupled to the transducers is provided to process the signals supplied to it, which signals then drive the first electroacoustic transducer or transducers, either directly or indirectly. A program for audio playback and a program for hands-free operation are stored in a program memory—the program for hands-free operation being loaded in the signal processing unit and run by this device during hands-free operation, and the program for audio playback being loaded and run by this device during audio playback.

[0007] In a modification of the invention, the signal processing unit has a device for automatic noise-dependent signal optimization, which analyzes the noise in the vehicle interior and modifies at least the volume in audio playback mode of an audio signal supplied to the signal processing unit for transmission. In devices of this type for automatic noise-dependent signal optimization, for example, the acoustic listening signal, composed of an acoustic useful signal and acoustic noise signal, is picked up in the vehicle interior by a microphone and, for example, separated into these two components. These components are then analyzed in comparison with the original electrical audio signal and a correcting variable is derived from them applicable, for example, to volume, degree of compression, and tone.

[0008] Preferably, the second transducer (such as a microphone) provided for the hands-free operation is utilized here during audio playback to capture noise in the vehicle interior. This approach requires the use of only a single second transducer (such as a microphone) which in hands-free operation essentially functions to capture speech signals from the operator, and in the audio playback mode captures noises in the vehicle interior. As a result, either a significantly better microphone may be employed for the same cost as two microphones currently, or costs may be significantly reduced (for example, by half) for the same transducer quality.

[0009] In addition, at least a first transducer (such as a loudspeaker) provided for the audio playback mode may also be employed for hands-free operation. Here again, the enhancement in quality is significant as compared with known systems, while in addition costs are reduced as compared with current systems.

[0010] Preferably, a mobile telephone device (permanently installed or portable) is connected to the audio playback device. The connection between the telephone device and signal processing unit may, for example, be implemented through a MOST bus and/or an optical ring. A MOST bus in connection with an optical ring is frequently employed, for example, to connect audio signal sources to a signal processing unit, so that a retrofit of this type on a mobile communications device may be implemented at low cost while providing a high level of compatibility.

[0011] Specifically, the telephone device is able to generate a receiver off-hook signal (cradle signal) and relay it to the signal transmission device. In response to the receiver off-hook signal, the hands-free program is loaded and run—otherwise the audio playback program is loaded into the signal processing unit and run by this device.

[0012] The receiver off-hook signal indicates whether or not a telephone call is currently in progress or is about to be initiated, and any music playing is appropriately switched off during the call so as to ensure the best possible transmission of speech. This means that when the receiver is taken off-hook, or a comparable action occurs (pressing the appropriate button), the audio playback is stopped, the hands-free program is loaded and then continues to be run as long as the receiver off-hook signal is being generated, that is, as long as the telephone call continues (“receiver is off-hook”).

[0013] When the receiver is hung up, or an analogous action is effected (for example, pressing an appropriate button), the hands-free program is interrupted, the audio playback program is loaded and continues to run. Since, as mentioned above, placing a call and, for example, listening to music are not allowed to occur simultaneously, the signal processing unit is able to be utilized in an optimal manner as a result of being activated in the two operating states in response to appropriate program control.

[0014] In addition, provision may be made for the telephone device to generate a ring signal and transmit it to the signal processing unit, so that the program for audio playback is interrupted when the ring signal occurs and continues, for example, after ringing ceases unless the receiver is taken off-hook.

[0015] Finally, a signal processor is preferably used in the signal processing unit since such a processor provides a high degree of flexibility. The appropriate program is then loaded from the program memory (for example, ROM) into the processor's program memory (for example, RAM). The advantage here is that the generally very high-performance signal processor provided for audio signal processing is also available for the hands-free operation, thus providing a significantly higher quality than is the case when employing the signal processors conventionally used in mobile communications devices.

[0016] The following discussion explains the invention in more detail based on the embodiment illustrated in the individual figures of the drawing.

[0017] In the embodiment shown, a signal processing unit SPU is provided. Connected to this device is a microphone MIC serving as an electroacoustic transducer to convert acoustic signals into electrical signals. In addition, two loudspeakers LSL, LSR (or groups of loudspeakers) are connected to the signal processing unit SPU, with the loudspeakers serving as electroacoustic transducers to convert electrical signals into acoustic signals.

[0018] The signal processing unit SPU contains, among other things, an analog-to-digital converter ADC, a digital signal processor DSP, two digital-to-analog converters DAC1, DAC2, two power amplifiers AMPL, AMPR, a nonvolatile memory ROM, and an interface BUS. Here the signal from microphone MIC, attached at an appropriate site within the vehicle interior, is fed to digital signal processor DSP via interconnected analog-to-digital converter ADC. The microphone is placed so as to permit effective capture of interior noise, yet also enable satisfactory pick-up of speech in the area of the driver position.

[0019] Digital signal processor DSP in turn feeds the two loudspeakers LSL and LSR via interconnected digital-to-analog converters DAC1, DAC2 and power amplifiers AMPL, AMPR.

[0020] Digital signal processor DSP is also connected to nonvolatile memory ROM through an address bus and a data bus AB, DB. Finally, interface MOST is coupled through a control line CL to the nonvolatile memory RM¹ as well as to digital signal processor DSP through a ring signal line RS, this line being either separate or combined in a bus, to a receiver-off-hook signal line HS (off-hook signal line), and to at least one audio signal line AS for the purpose of transmitting audio signals. Externally, interface MOST is connected through a bus line BUS to a mobile communications unit MCOM, for example, a CD player, and a radio receiver CUN. One example of a possible bus line is an optical ring. Mobile communications unit MCOM, CD player CDP, and radio receiver TUN here may be designed so as to be combined with signal processing unit SPU, each as a separate entity, or in combination.

[0021] Digital signal processor DSP includes a volatile memory RAM in which the currently running program is stored. The determination as to which program is loaded into volatile memory RAM from nonvolatile memory ROM is made by a selection unit which is implemented either in the digital signal processor DSP itself or externally to the digital signal processor. Based on the signals provided by the interface MUST², specifically, the receiver off-hook signal HS, selection unit SU determines which program is required, loads this from nonvolatile memory ROM into volatile memory RAM, and then launches the program just loaded.

[0022] This embodiment accomplishes this either by using hands-free program HFM or audio playback program AUN³ in combination with a program for dynamic sound optimization DSO. Control by selection unit SU is effected here such that audio playback program AUM is operated with or without the program for dynamic sound optimization DSO. If ring signal RS occurs, audio playback program AUM is interrupted, and, for example, a ring tone is put out through loudspeakers LSL and LSR. If the receiver is not taken off-hook, digital signal processor DSP returns to audio playback program HUM⁴ upon termination of the ring.

[0023] When the receiver is taken off-hook (with or without the preceding ring signal), audio playback program AUM is terminated, hands-free program HFM is loaded from nonvolatile memory ROM into volatile memory RAM, and hands-free program HFM is launched. Preferably, microphone MIC, normally used for dynamic sound optimization (DSO), is utilized as the hands-free microphone. In addition, the two loudspeakers LSL, LSR, normally used for audio playback, are utilized as listening loudspeakers.

[0024] Any of a number of conventional techniques may be employed in the program for dynamic sound optimization, such as those disclosed in U.S. Pat. No. 5,434,922, U.S. Pat. No. 5,615,270, GB 2,248,001, EP 0 319 777, EP 0 141 129, etc. Similarly, any of a number of hands-free techniques, such as those disclosed in U.S. Pat. No. 4,912,758, U.S. Pat. No. 4,965,822, U.S. Pat. No. 4,982,427, and U.S. Pat. No. 5,054,061, may be employed as the basis for the hands-free program. Techniques used in audio signal playback include, specifically: filter routines, compression routines, and attenuation routines, etc. 

1. Circuit for audio playback and hands-free operation in a motor vehicle including: at least a first electroacoustic transducer (LSL, LSR) to convert electrical signals to acoustic signals, a second electroacoustic transducer (MIC) to convert acoustic signals to electrical signals, a program-controlled signal processing unit (SPU) coupled to the transducers (LSL, LSR, MIC) to process the signals supplied to it to effect a driving function, and a program memory (ROM) that stores a program (AUM) for audio playback and a program (HFM) for hands-free operation, for the signal processing unit (SPU), wherein the program for hands-free operation (HFM) is loaded into the signal processing unit (SPU) and run by this device during hands-free operation, and the program for audio playback (AUM) is loaded into and run by this device during audio playback.
 2. Circuit according to claim 1, in which the signal processor device (SPU) has a device for automatic noise-dependent signal optimization (DSO) which analyzes the noise in the vehicle interior, and in the audio playback mode (AUM) modifies at least the volume of an audio signal supplied to the signal processing unit (SPU) for transmission.
 3. Circuit according to claim 2, in which the second transducer (MIC) provided for hands-free operation is employed in the audio playback mode (AUM) to capture noise in the vehicle interior.
 4. Circuit according to one of the foregoing claims, in which at least a first transducer (LSL, LSR) provided for the audio playback mode is employed for hands-free operation.
 5. Circuit according to one of the foregoing claims, in which the one mobile communications device (MCOM) is connected to the signal processing unit (SPU).
 6. Circuit according to claim 5, in which the communications device is connected to the signal processing unit (SPU) through a MOST bus (MOST).
 7. Circuit according to claims 5 or 6, in which the communications device is connected to the signal processing unit (SPU) through an optical ring (BUS).
 8. Circuit according to one of claims 5, 6, or 7, in which the communications device generates a receiver off-hook signal and transmits it to the signal processing unit (SPU), and in which the program for hands-free operation is loaded into and run by the signal processing unit (SPU) when the receiver off-hook signal occurs, whereas otherwise the program (AUM) for audio playback loaded into and run by this unit.
 9. Circuit according to one of claims 5 through 8, in which the communications device generates a ring signal (RS) and transmits it to the signal processing unit (SPU), and in which the program (AUM) for audio playback is interrupted when the ring signal (RS) occurs. 